With the development of computer network technology and the boom of online shopping, a lot of shopping sites have appeared. Sellers typically register with a shopping site, upload commodity information and complete the transactions at home.
For example, presently the shopping site taobao.com has 180 million items for sale (also referred to as commodities). Each commodity released by a seller has its corresponding name, picture, brief description, price range and related properties. Since the same product may be released by multiple sellers as multiple commodities, there is a lot of redundancy in the data of these commodities. Take the Nokia N73 mobile phone for example, each time a seller releases a Nokia N73 phone as a commodity, the corresponding picture(s), description of the product, the functions and other information are entered by the seller and stored. When a large number of sellers are selling the same mobile phone, a great deal of duplicate data is stored. Since the typical shopping sites use databases to store the commodity entries, maintaining a large number of commodities in the database can be expensive.